Overview
The Tennessee and Cumberland River basins historically contained the greatest diversity of freshwater mussels anywhere in the world. Species specific to this area are referred to as “Cumberlandian”. The shiny pigtoe is a Cumberlandian species restricted to the middle and upper Tennessee River system and has always been considered rare. It was placed on the federal threatened and endangered species list in 1976 as endangered.
There are currently five known populations of shiny pigtoe – one in the North Fork Holston River in Virginia, one each in the Clinch and Powell rivers, both crossing the Virginia-Tennessee state line, one in the Elk River in Tennessee, and one in the Paint Rock River in Alabama. The species was recently rediscovered in the Elk River, it had not been seen in approximately 35 years prior to collection in 2021. Initial steps have been taken for it to be reintroduced to the Tennessee River in Alabama and the lower Holston and French Broad rivers, both in Tennessee.
All surviving populations continue to be threatened by many of the same factors identified at the time of listing e.g., habitat fragmentation, loss, and alteration resulting from impoundments; operation of hydroelectric dams; mining; wastewater discharges; water withdrawal; competition and displacement by non-native species; and the runoff of silt and other pollutants from ground disturbance activities.
Scientific Name
Identification Numbers
Characteristics
Habitat
The shiny pigtoe is associated with clean, fast-moving water with relatively stable cobble, gravel, and sand substrates free of siltation. The mussel is usually found buried in the substrate in shallow riffle, ford, and shoal areas but can also occur in deeper runs.
A natural body of running water.
Food
The shiny pigtoe is a filter feeder, feeding by straining small organisms and food particles from the water.
Physical Characteristics
A medium-sized mussel that is about 2.5 inches in size. It has an ovoid shell; the hinged end of the shell is rounded with a straight front margin. The valves are subtriangular, and beaks turned forward and anterior to the midline with deep cavities.
The smooth and shiny shell has distinguishing dark green to blackish rays on a yellow to brown background. Younger specimens have a bolder ray color patterning. The inner shell surface is white.
Life Cycle
The lifecycle of the shiny pigtoe is like other river mussels. Males produce sperm which are discharged into the water and dispersed by currents. Any downstream female of the same species obtains these sperm during filter feeding. Fertilization of the female’s eggs by the sperm occurs within the gills of the female. The fertilized eggs are retained in brood pouches, which are a modified section of the gills, to develop into larvae called glochidia. Once developed the females release the glochidia into the water. The glochidia must attach themselves to an appropriate fish host. After riding around on the fish for several weeks the glochidia will fall off the fish and settle on the bottom of the river or stream.
The shiny pigtoe is a short-term brooder. Short-term brooders breed in the spring and early summer and release glochidia by mid to late summer.
Similar Species
Geography
The shiny pigtoe historically occurred throughout the middle and upper Tennessee River drainage in the states of Alabama, Tennessee, and Virginia. When the Recovery Plan was written in 1984, there were five populations, however one, the Elk River in Tennessee, has disappeared. The Clinch and Powell River populations straddle Virginia and Tennessee. The North Fork Holston River/Copper Creek population is in Virginia. The shiny pigtoe is also in north Alabama’s Paint Rock River.
Timeline
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